Since 1980 the weight of the average female has increased by more than a stone (6.35kg) – leapfrogging countries including Spain, Italy, and Germany.

At the start of the 1980s, the average 5ft 3in British woman weighed 10 stone (63.5kg), but by 2008 that had grown to 11st 2lb (70.6kg).

Only Malta and Israel – which was classified as Western Europe for the purposes of the report, published online today in The Lancet – now have fatter women.

The global study compared the average body mass indices (BMIs) of men and women in 199 countries.

It found British women's BMI had increased from 24.2 to 26.9, up from 12th equal fattest out of 23 nations, to third place. British men fared little better, with their BMI rising from 24.7 to 26.6, taking them from 17th to fifth place. Of the main Western European nations, only Spanish men are fatter. The weight of the average British 5ft 9in man has risen from 12 stone (76.1kg) to 12st 12lb (81.9kg).

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Doctors prefer BMI because it takes into account a person's height. It is calculated by dividing one's weight in kilograms by the square of one's height.

The "average British couple", if they exist, are now officially too fat for their own good. Under Department of Health guidelines, most adults should have a BMI of between 18.5 and 25. A BMI of between 25 and 30 is classed as overweight, while over 30 is obese.

Numerous studies have found that people who are overweight or obese have a higher chance of developing heart disease and certain cancers.

Tam Fry, of the National Obesity Forum, said successive governments since 1979 had undermined public health, by "feeding children junk food in school, selling off playing fields, and failing to tackle the food industry".

• Almost 80,000 cancers could be prevented in Britain every year if everybody followed a healthy lifestyle, such as walking for half an hour a day, maintaining a healthy weight and eating a healthy diet, the World Cancer Research Fund has estimated.